The long term objective of this project centers on the study of the intermediate cascade of biochemical and cell physiological mechanisms that lie between initial bioactivation of hepatotoxins and the ultimate pathological consequences of such bioactivation. The central hypothesis guiding past and projected work is that the overall mechanism of action for a wide variety of hepatotoxins involves a toxigenic sequence characterized by a rise in cytosolic free calcium ion and activation of phospholipase A2 (PLA2) and cytosolic proteases leading to degeneration of the cell membrane and death of the cell. Most of the work will be carried out with suspensions of hepatocytes exposed to carbon tetrachloride and other agents known to alter calcium homeostasis and stimulate PLA2 activity including bromotrichloromethane, chloroform, and vinylidene chloride. Because the toxicity of CCl4 is greatly enhanced at low PO2, projected studies conducted at reduced PO2 should provide new data on the key question as to whether an increase in cytosolic free Ca2+ and the activation of PLA2 and proteases are essential steps in the overall pathologic sequence. Proposed studies at low PO2 may reveal a toxigenic disturbance of a prostacyclin-thromboxane balance in hepatocytes exposed to toxic agents such as CCl4. An examination of the modulating effects of cytoprotective prostaglandins, PGI2 and dmPGE2, on the key steps in the CCl4-toxigenic cascade, viz., rise in cytoplasmic free Ca2+ levels, PLA2 and protease activation and the relationship of these parameters to cell blebbing and death is planned.